Three-dimensionality effects on the flow past a horizontal heated cylinder under mixed convection heat transfer

Abstract

The three-dimensionality has a significant effect on the flow-field and heat transfer, especially when the geometry is affected by thermal buoyancy. In the present research, the interaction of three-dimensionality, thermal buoyancy, and vortex shedding on the flow around an isothermal horizontal cylinder and its mixed convection heat transfer were numerically investigated. Both the secondary flow due to the thermal buoyancy and the free stream had an upward direction. The problem was simulated in a constant Prandtl number of 0.7, a range of Reynolds numbers (based on the cylinder's diameter) between 100 and 300, and Richardson numbers ranging between 0 and 0.5. The aspect ratio of the cylinder was 6. The numerical simulation of the problem was based on the discretization of the Navier–Stokes, energy, and k–ω SST turbulence equations. A finite-volume and pressure-based method with second-order spatial and temporal accuracy was utilized. The momentum, energy, and turbulence equations were explicitly solved, while the pressure equation was solved, implicitly. Comparison of the two-dimensional and three-dimensional simulations showed that the thermal buoyancy had a significant impact on the flow three-dimensionality, so that the flow could become three-dimensional even at low Reynolds numbers such as Re = 130. In addition, the results demonstrated that for each Reynolds number, there was a critical Richardson number where the mean drag coefficient and Nusselt number reached their minimum value. Moreover, for Richardson numbers higher than the critical value, the flow entered a new low amplitude vortex shedding mode.